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How to / DIY => Everything else => Topic started by: BruceM on July 04, 2021, 07:30:42 PM

Title: Lithium cell balancing
Post by: BruceM on July 04, 2021, 07:30:42 PM
I've noticed that LiFePO4 cells direct from China have come down quite a bit.  So I've been researching how to best handle cell balancing for a 120VDC battery bank (39 cells in series operated from 119V to 132V. (3.4 to 3.05V)  I've got a few years to get ready for the switch.

I wondered if Starfire or anyone else might chime in on homebrew designs?  I am familiar with the various commercial  balancing products, but they generate a lot more EMI than I'd like.  The modest current, passive balancers are lowest EMI but still it is connecting a microcontroller with SPI interface to all the cells.
Title: Re: Lithium cell balancing
Post by: mike90045 on July 06, 2021, 06:16:34 AM
I would prefer not to use balancers, but to order some extra batteries with the initial order, and then sort/bin the batteries, so you build a bank with all matched batteries, and top or bottom balance the bank.   (and hold in reserve the low capacity & high capacity cells )
Then just rely on the BMS to monitor cells in case one fails.
Title: Re: Lithium cell balancing
Post by: BruceM on July 06, 2021, 07:48:56 AM
Some folks do nothing but manual  monitoring and balancing every few weeks, even months for the first year or so.  I think I'd like something automated.  I'm not getting younger.


 I'm now thinking that some passive top balancing (fixed voltage load switch type) and modifying my big linear PV regulator to be fixed voltage might suffice.  The commercial ones are very cheap but the trip voltage is preset too high for my planned scheme.  The ones sold for bike packs are only 35ma of discharge, only when the batteries are full and still on the charger. That's not much time or current.  For my off grid PV system, it would be most of the day every day, so might work out even at 50ma.

I've never used lithium cells at all so lack the practical experience with them despite doing a lot of reading on BMS/balancer designs. 

My experience with my own linear 12V battery regulators is very positive; the batteries last a long time and I can swap in a new battery without trouble.   I could implement the same thing for lithium cells, though it might be much more than is needed, and with 38 or 39 regulators needed, it's quite an expense and build!




Title: Re: Lithium cell balancing
Post by: mike90045 on July 07, 2021, 07:15:53 AM
This is a well written, correct article about setting up a Li bank
http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/
  enjoy
Title: Re: Lithium cell balancing
Post by: BruceM on July 07, 2021, 07:58:37 AM
OK on the basics but he is not mentioning battery balancing hardware, even though the photo of the 4 cell pack clearly shows a balancing cable hooked up for a battery balancer. 

Daly makes a decent 4 cell LiFePO4 basic one for cheap, I just don't care for the added EMI of that type with a microcontroller.  There are also plenty of  balancers with current and low voltage protection as well, for 12, 24, and 48V packs.  It more serious money for a balancer for 39 cells in series, and again comes with EMI issues I don't want.

Because my bank is full every day, most of the day, I think a simple passive top side shunt regulator or top voltage switched load resistor should suffice.  Because of the number (39) required, I'm trying to resist the urge to get fancy.

Title: Re: Lithium cell balancing
Post by: BruceM on July 12, 2021, 11:28:35 PM
I joined a DIY solar form to solicit experience with LiFePo4 cells.  It seems that claims of 10 year plus are fantasy. One retired EE circuit designer made an impressive 100V series string and balancer, his own inverter.  In three years with new balanced cells and modest DOD, he's had 3 of the 30 cells fail suddenly and without warning, as a complete short (dead), the first in a year. That's 10% failure rate in 3 years. And these were very expensive batteries with a very sophisticated BMS/balancer.   A friend of his who bought a set from the same supplier had the same experience.  Of course, the seller says it's never happened.  Uh huh.  The retired EE is planning on switching to refurbished forklift batteries at 48V.

It seems that LiFePo4 is not quite there yet in durability and reliability, once you get past the new adopter enthusiasm/delusions.

Title: Re: Lithium cell balancing
Post by: 32 coupe on July 13, 2021, 04:21:21 AM

I wondered what was what when you first brought this subject up. I thought I'd wait to comment.

Chinese batterys ? Really ?

I don't think you can buy ANY good batterys anymore. (Yea, I'm sure I'll catch *** for that.)

I am in the marine industry and haven't had good luck with any of the major brand batterys.
About 2 years is the new norm for battery life. Wet, mat, gell....they are all junk.

I have owners ask about  lipo's etc. all the time. A while ago I asked a friend who I consider to
be an expert on batterys, chargers, solar etc about them and he says the problem is that their are
not really any  "standards" for most of the newer compounds in batterys and that the charge and
maintenance schedules are all over the place.

Unless one wants to go down the "virgin lead" road throw away batterys are here to stay.

I wish you could buy good batterys at a reasonable price today. I remember ( here we go !)
when the average car battery would last for years. My daily driver truck seems to eat a battery
on a 2 year cycle. Not cheap baterys either. The guys I work with seem to have the exact same
results. The last couple have gone dead suddenly. Start fine for months then BAM dead.

There is so much junk out there today you never know what you are getting. Especially from China.
I have gotten pretty cynical the last few years. Terrible service and no warranty seem to be the new
industry standard. That new battery with the fancy plastic case and bright shiney colors might just
as well be a gold plated t**d. And don't even bring up cost.....thru the roof !

Bruce, I thought you were using "cycled" fork lift batterys ? I'd stick with that and save your money.

Now if you run across those tall batterys used in back ups for com towers and crash carts grab them.
I haven't used them but have seen excellent reviews for them. I remember pricing some for a customer
a couple of years ago and he went with standard wet cells after seeing what those "virgin lead" batterys cost !





OK, rant over. Let the stones fly !

Gary




Title: Re: Lithium cell balancing
Post by: BruceM on July 13, 2021, 07:07:35 AM
I'm using wet lead-calcium, "marine deep cycle" batteries, ten in series for 120VDC.  Because my DOD is so low, they last 4.5 to 5 years.
They only need a bit of water once a year, and float current is under 0.1 amp. 

I have zero interest in the fork lift batteries; 100Ah batteries are plenty for me, I'm only using  20AH.

My battery bank replacement cost is now up to $1000., every 4.5 years.  That's not bad, a fraction of what my neighbors with 48V L16 banks pay, and longer lived as well.



 
Title: Re: Lithium cell balancing
Post by: mikenash on July 13, 2021, 08:21:04 PM
Hey Starfire I wonder if you would like to chime in here?

It's a topic that interests me too as I need to deal with a situation where solar-charged batteries are often unused & unattended for weeks/months, and where they can be charged at sub-zero temps on a crisp, sunny winter's morning

I know you know what you're talking about; and I guess you have a couple of years under your belt using the new LIFEPOs

Cheers, Mike
Title: Re: Lithium cell balancing
Post by: BruceM on July 13, 2021, 09:02:34 PM
Mike, you just can't charge most LFP/LiFePo4 batteries below 0C.  Most the better BMS hardware automatically disconnects the PV regulator input at that temperature, as it will wreck the batteries.  Another issue is that a BMS failure can also result in the destruction of your battery bank; a concern for unmonitored or remote situations.

So LFP/LiFePo4 wouldn't be a wise choice for your application, besides the cost of the batteries sitting there for the taking while you're away.

I'm not sure why Gary (32coupe) is having such bad battery experience.  New cars tend to eat batteries more today because of so much "always on with ignition off" electronics load.  Perhaps in boats as well.  Heat is another well known battery killer, and virtually no auto or marine battery charge regulators bother to do temperature compensation.  So batteries in hot climates are getting overcharged to death, and just sitting in the heat, the batteries are aging prematurely. 

I've gotten consistently good service on both single AGM and wet Marine type batteries for my big 120V battery.  I get 6.5 years life on the former and about 4 to 5 years on the latter.  I'm on my 3rd AGM and  my 4th of the marines.  My neighbor has the same setup and gets the same service.  I bought my latest set 6 months ago, a bit early at 4 years but he was at 5 years so we got a good bulk buy deal on 20 at our nearest Car Quest.  We both use temperature compensated charge controllers and a battery balancing system on the large battery string.

Bruce


Title: Re: Lithium cell balancing
Post by: 32 coupe on July 14, 2021, 05:50:15 PM

I know heat does play into the life span.
It gets HOT in florida !

 
Title: Re: Lithium cell balancing
Post by: MachineNLectricMan on October 31, 2021, 12:29:46 AM
I have a lot of experience with lead acid battery technology, to the point of in depth knowledge of their manufacture, and it is rare that a new technology comes along that is better, but I am convinced that the LiFePO4 is the way of the future. Lead acid technology is extremely sensitive to abuse and depth of discharge. There are some that will last twenty years if correctly managed, but one screw up and that is lost. Be prepared to spend 10k to 20k dollars to get a decent sized bank with the 25% max depth of discharge limit for this lifespan. There are (or were) only about three companies in the world that made true deep discharge batteries that are a spin off from the old submarine battery technology. Only two remain in North America, one is in Kalifornia, the other in Kanada. (spelling no accident). There were a few overseas. All other manufacturers offer deep cycle imposters which are basically modified engine start batteries labelled as deep cycle.

The LiFePO4 batteries however are not nearly as sensitive to depth of discharge as long as they are never discharged below 2.5v per cell, and most batteries are capacity rated with this limit as fully discharged. They need to have electronic managing to prevent this but one control can manage the entire bank. There is the 0 degree temperature limit for charging (but not discharging), but really...... how hard is it to provide minimal heating for a battery bank? If well insulated in winter, most banks will be self heating anyway. These batteries are less than 1/4 price of the same size equivalent of lead acid (at the 25% DOD limit!). The LiFePO4 technology does not have the thermal runaway problems that the other lithium technologies have. This is one of the reasons Tesla has recently chosen this technology for future cars. You pretty much have to intentionally heat them artificially to get a thermal runaway.

Balancing? I am humored to see all of the electronic "contraption" circuits people have come up with for this. Turns out that there is a DIY or "redneck" solution that is extremely simply. The only difference between lead acid and LiFePO4 is that lead acid technology "self balances". Both battery technologies actually required balancing! When charging lead acid batteries, after a certain voltage is reached the electro-chemical reactions begin to cause water to be broken into Hydrogen and Oxy.. This process allows current to leak through the charged cells that charges the cells that are lagging behind. In LiFePO4 technology this must be provided artificially, but does allow voltage mode charging the same as finish charging lead acid batteries. It also turns out that 4 LiFePO4 cells charge at the same voltage as 6 lead acid cells which allows the same charger to be used!

OK how do we do this? Turns out that low voltage zener diodes have a very wide "delta zener" range, which all established electronics designers are warily aware of.  A 3.3v zener gives just the right amount of bypass current at 3.6 volts to emulate lead acid self balancing. And just like the contraption circuits using mosfets, etc out there, the zeners are connected across the terminals of each cell so that the zener current direction is shorting the cell. (diode band towards the positive). After fully charging, disconnect them as they will leak discharge some of your battery capacity. Use 3 or 5 watt 3.3v zeners. Also, with the size of the battery banks used in off grid, the zeners will act as self fuses if anything goes wrong and you overheat one. I.E. The diode will fail shorted then mechanically melt and open.

Keep in mind that discharging below 2.5v or charging over 3.7v per cell will cause dendrites to begin to form internally which will cause a major cell failure if that condition continues very long. Same with charging below 0 C..

In my opinion, the price of these will continue to drop and they will become almost "disposable". The caveat is only china is making them. Tesla is currently getting them from china, but Tesla is also in the process of build a US plant to make these! Question is, can anyone in the public get these from Tesla, and will Tesla's prices be reasonable and affordable? China has very dicey quality issues, some times you can get good stuff, sometimes really bad stuff and you never know which on any particular order.  Also, individuals have no market leverage when ordering from china and may have difficulty in correcting any quality complaints.
Title: Re: Lithium cell balancing
Post by: mikenash on October 31, 2021, 06:15:42 PM
Still watching this topic with interest, thanks
Title: Re: Lithium cell balancing
Post by: Fred8 on November 02, 2021, 01:29:59 PM
Lead acid technology is extremely sensitive to abuse and depth of discharge. There are some that will last twenty years if correctly managed, but one screw up and that is lost.

There is a lot of BS written to promote Lipo ( all lithiums)  and disparage LA and this is some of it.
Lipo is FAR more unforgiving than Lead and sorry, anyone that said otherwise has no experience with the 2 technology's or is flat out lying/ Biased.

Run a Lipo dead flat and try and recover it. Extremely unlikely and if you can it will have bugger all capacity.  Run an LA dead flat and you'll recover it easily and the capacity fall off will be very small IF you only do it once.  Then again, once is all you would get to do it with lipo, no question of that.

Same token, over charge a Lipo and see what happens with that when it swells up and maybe lets the magic smoke escape.  I have BOILED  LA and for some hours and put a load on it to take the overcharge off and they batteries were fine. Not saying there were completely unscathed but they ran as normal  afterwards and only required a bit of a top up.  Not like you can determine a time how long any battery will last to say how much it's life was shortened but with Lipo, one way or the other too far and its game over, dead and buried.


 
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Be prepared to spend 10k to 20k dollars to get a decent sized bank with the 25% max depth of discharge limit for this lifespan.

I cannot comment on pricing where you are but that's ridiculously over the top for where I am unless you are talking about some pie in the sky technology or an unnecessarily large pack.

The bit about 25% Discharge is  regularly recited complete and utter BUNK!

 LA traction ( forklift) batteries are WARRANTED to  not below 80% DOD.  That is , for complete clarity, if you have a 100Ah battery you can take 80 Ah OUT of it  EVERY DAY and that's what the manufacturers warrant it for. 
This is easy to verify, just go to any traction battery manufacturers website and look it up. This 25 and 50% DOD for LA is ignorant Rubbish.
This isn't car batterys we are talking about or some other unfit for purpose type. Then again, even decent car starting batterys wouldn't' be terribly phased  by 30%  discharge especially if they were deep cycle which will handle 50% or better DOD. 

I really don't know why people continue to spread this complete and utter BS about LA batteries nor make out the Lithiums are capable of things they are not. it's misinformation that only causes people to make wrong assumptions and prevents them getting what best suits their needs and is completely unhelpful.  They are batteries for hecks sake, not your children you are trying to get into College. They both have their strengths and weaknesses like anything but why try to make them out something they are not? I don't ever get it but see it all the time.

Where I am, warranted 48V, 720 Ah Fork packs can be had for around $4000, often less.  They are gauranteed for 5 years for solar use provided they are not discharged below 80% . The manufacturers I have spoken to love selling them for solar use.  The current pulled out of them is typically much less, they are not subject to banging and vibration, not discharged nearly as much or run till the shift is over no matter how low they are, usualy set up with auto watering systems, don't have the max charge belted into them in order for them to be ready in the morning or for the next shift and overall have a Much easier life.

One Guy I spoke to said he'd never had a claim with any he sold for off grid use, wished he could say that for their intended application!
Lipo may have some advantages over LA like weight and size which is irrelevant in a stationary application anyway but in Bang for the buck stakes, LA craps on  Lipo.  From what I have read, also does in reliability and longevity.  Read of plenty of people whom have babied the things and they have fallen over in under 4 years.

I have also read miles of BS about lipo taking much higher charge rates than LA.  Again, largely BS. You can't just pump limitless power into lipo at all, not without shortening it's life of course.  OTOH, while LA is Limited in charge rate, the amount of power that works out to on a 6 or 700AH pack is more than anyone is likely to have on their roof in panels unless they are running a solar farm.
Even running .2C is going to be 140A on a 700ah pack and they can take a lot more than that on bulk charge.  How much solar or how big is your generator again?  Also read repeatedly that lipo can be charged at a flat full rate till it comes up to Voltage. Yeah, but it's going to cut the life significantly. In reality they should be given a bult and then a top off charge at a reduced rate similar to LA.  IF you want best life that is.


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The LiFePO4 batteries however are not nearly as sensitive to depth of discharge as long as they are never discharged below 2.5v per cell,

And if they are run below 2.5, they WILL Be damaged and maybe unrecoverable depending how low they get.
Not a good idea to Run LA right down either but they WILL recover from it. read PLENTY of reports of people that have locked up their Lithiums through over discharge and can't get even months old packs back up.  Only takes a BMS failure and they are bricked.


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These batteries are less than 1/4 price of the same size equivalent of lead acid (at the 25% DOD limit!).

Again, maybe where you live when you work on BS figures like 25% DOD for the LA but I have YET to see any decent lipos cheaper on an AH basis than LA unless you are talking those Chinese Cheapies that are all the rage and have dozens and dozens of Documented failures on Forums. I have seen a lot of people that make this cheaper than LA Claim but they are inevitably quoting 2nd and 3rd rate batteries in chyna and not including delivery and all shipping costs.   And of course if a cell is bad or goes tits up, you are waiting months for a replacement IF the seller Honours any warranty  if there was one and you are undoubtedly up for more shipping and customs costs.
With a fork pack, go to your nearest company and get a standardised replacement off the shelf. Drop the failed cell off at the local Scrappy and you'll get 25-33% of the price of the new cell back.

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In my opinion, the price of these will continue to drop and they will become almost "disposable".

Another forum fan boi myth.
There is a HUGE demand for  batteries world wide especially the lithiums. They are bing put in everything these days.  Tesla for one can't get enough and the production of these EV's  is ramping up despite the ignorance of people thinking they are cleaner than FF vehicles increasing demand.
The production of raw materials for Litho type batteries is very limited and mainly carried out in  3rd world politically unstable hell hole countries that have little to no environmental rules and enforcement which makes it infinitely cheaper to process there than bring the materials into first world countries where enviro regulations make the cost far higher.  One little conflict in these countries and production ceases and prices skyrocket.

I have NEVER seen anything in short supply through high demand get CHEAPER  in price.  Does not happen.

If one takes case in point, tesla power walls keep going up in price, around $1000 last year and the year before.  Not aware of ANY battery coming down in price for that matter.
Lipo is as cheap as it's going to get right now.  Add in supply chain problems from Convid and offshoot factors and there is no way  these batteries are going to get cheaper in present chemistry and if something new comes along that will have the elevated introductory costs for a few years as well.

As far as Disposable, that's a good point.  LA here is worth presently about a 3rd to quarter of it's purchase price as scrap which is also a factor in being better bang for the buck over lipo .  There are limited lipo recycling facilities at this time, more in some countries than others but some places are already talking disposal fees for these batteries due to their Toxic nature.  LA can be recycled at any scrap yard, not many places relatively will take lipo.


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The caveat is only china is making them.

Bingo and as you allude to, the quality is HIGHLY suspect.  I see most of the fanbois on solar and RV forums are all over the cheap, 2nd quality cells and the outcomes with them are hit and miss at best. If you miss, it's a lot of money down the drain or a long downtime and more cost to get a replacement... which will then never balance with the rest of the pack due to age alone.

 
Quote
Tesla is currently getting them from china, but Tesla is also in the process of build a US plant to make these! Question is, can anyone in the public get these from Tesla, and will Tesla's prices be reasonable and affordable?

Tesla and other car manufacturers are saying and have been for some time that supply of batteries is both their biggest limitation, headache and expense in the vehicles.  If they can't get enough to satisfy their own needs (Powerwalls were halted from production for many months because of Cell shortages) They certainly won't be offering them to the public to compete with their own products and if they did, they would certainly not be cheap.  NOTHING with Tesla ever is and they would put huge markup on anything with their name attached anyway.


 
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China has very dicey quality issues, some times you can get good stuff, sometimes really bad stuff and you never know which on any particular order.  Also, individuals have no market leverage when ordering from china and may have difficulty in correcting any quality complaints.

Agreed but this should have been your preface paragraph because it' is the relevant and over riding thing to everything else you said.
what good is cheap and whatever else benefit if it's unreliable or short lived?

All this " In the future" stuff is all well and good to say something will improve but it in effect never comes about because then something new comes along and it's back to square 1.
These Lipo technology's are a prime example. Every time they change the formulation  it's back to the beginning again. No one knows how they will hold up in 3-5-10 years time and what the last formulation did is irrelevant because this one is different and unknown.

La OTOH being old fashioned and untrendy and heavy and bulky and all that IS well proven, known and understood.  I know people personally that have had over 15 years out of proper traction batteries.  I asked a Client of mine about the  La " Maintenance Myth. He said he shuffles down the shed every 3 Months or so to put a bit of water in the automatic watering system and make sure the rats haven't  done anything. He says a guy comes out every 12 Months, checks the gravity of the cells, removes, greases and replaces the leads and wipes them down with a rag to get the dust off and make them look pretty again. 

He's been running his farm off grid for nearly 50 years and figures on 2-3 Inverters per set of batteries. He ran a Moffit Generator  and then went to panels in the very early 80's.

I hear lots of people going on about " Maintenance"  Like it's an endless chore yet there is nothing like the time needed on them that people spend taking the trash cans out and brining them back in every week but no one sees that as some great hardship like they make out checking battery's every moth or 3 is.
Title: Re: Lithium cell balancing
Post by: BruceM on November 02, 2021, 06:10:30 PM
I enjoyed your post greatly Fred8, because I also disagreed strongly with the pseudo-technical content and attitude of the prior poster.  So much so that I avoided responding; I thought it a troll.

Regarding lithium LFP batteries, I found in pursing information on other engineering forums, I ran into another older EE like myself how had designed and built his own inverter and BMS/cell balancer. His was based on the very latest LiFePO4 cells at great expense.  He used a nominal 90VDC series string, and much to our mutual surprise, we had both done original inverter designs similar to the old Trace SW sine series.   

He used an original passive balancing design for his LFP cells which allowed him to see a display of all cell voltages to monitor them.  Since it was his own, new design, he monitored it closely.

Long story short, he'd had one cell die of sudden short every year for 3 years, and was so pissed at the unreliability of his  very expensive premium matched cells that he was considering changing his power system to locally available 48V fork lift batteries.  ​

I do expect that LFP cells will become more reliable in time; already some folks are very pleased with the reliability and lifespan of the very, very expensive BattleBorn 12V LFP batteries in marine applications (where size is a concern and cost is not so important.) 

Lastly, I'll add that 3 or 5 W, 3.2V zeners do not provide a useful non-manual  balancing system- for many reasons, such as connecting and disconnecting them manually  is a farce, and of course most would like more than 1 amps of charge rate, which is about all you could manage with a 5W zener.  Manual balancing CAN be used for new matched capacity cells, but that's not going to last for years or past the first bad cell that must be replaced.  To suggest this as a wonderful solution while denigrating others made me suspect a  troll.  Likewise the absurd notion that only US made submarine lead acid batteries are good when I'm surrounded by off grid homes all reliably and affordably run on a variety of LA batteries.

Not one company making LFP battery packs does NOT use individual cell voltage monitoring (high/low) and balancing. They don't do that for fun; they do it because it's needed.  But it's also true that a failure of the BMS/cell management circuitry can also cost you the entire battery bank, since as Fred8 points out, you are unlikely to recover an LFP cell once it's been over or under the allowable range of voltage. That is a well acknowledged fact, and it's why cell voltage monitoring is built into LFP packs; typically charging is disconnected when any cell goes to max voltage, and discharging is disconnected when any cell goes low.  This to required save the cell(s) from destruction. 

I found an example of such a disaster on one forum; A new DIY, LFP enthusiast was using a MPPT PV regulator, with a high voltage PV series string. A very common setup.  The MPPT, Buck type PV charge regulator failed short circuit (the typical Mosfet and  failure mode), applying the high voltage to the BMS.  The BMS was not rated for that high of an input voltage, so it's solid state (MOSFET) cut off switch also failed, as short circuit.  The LFP prismatic cells were then destroyed by excessive voltage.  The cell balancing hardware was also destroyed by too high voltage.  So a complete and total loss of well over $10K worth of new LFP batteries, all a cascade of destruction from a MPPT failure.

I'm hoping that the quality demands of automotive manufacturers will force rapid improvement in LFP quality and reliability, and the price of bargain B grade cells today will purchase reliable cells in the future.  I accept that I may still live out my life on lead acid batteries, and at what is now $17/month battery bank replacement cost, I won't lose sleep over that.  I won't switch until it becomes clear that it's cheaper for me to do so.


Title: Re: Lithium cell balancing
Post by: mobile_bob on November 02, 2021, 08:06:30 PM
this battery thing has been something that i too have given considerable thought to, a lot of research, and i too have concluded that the lithium batteries (and the variants) while showing promise look to be problematic for all the reasons previously discussed.

"if" one were to rethink his energy needs, i think an argument can be made for the simplicity and low cost of a system based on the lowly golf cart battery.

now if one wants all the modern creature comforts of modern living, then large traction batteries are likely something that is hard to beat, given a "complete" cost analysis (including risk factors).

"if" one gets really down in the weeds, and is willing to focus on an efficient system, with low cost per kw/hr, i can make a good argument for the automotive starting battery.  however not many folks want to get down into that level of use, or rather adapting to the system, rather than forcing a system to adapt to modern use.

we are probably still 10 years away from getting a quality lithium based battery, that is well protected and has a low risk of failure.  how low that risk factor gets is anyone's guess, and even if it does get to a low risk, that level of risk may well still be too high in the analysis.

in the end, it is hard to get a battery with the energy density of a gallon of fuel, as dependable, and at so low a price.  it appears to me that the lead acid battery still is a strong contender for stationary use.

bob g
Title: Re: Lithium cell balancing
Post by: Fred8 on November 03, 2021, 02:46:20 AM

Long story short, he'd had one cell die of sudden short every year for 3 years, and was so pissed at the unreliability of his  very expensive premium matched cells that he was considering changing his power system to locally available 48V fork lift batteries.  ​

I believe I know the gentleman you speak of.  I talk with him regularly.  IMHO the man is  an electronics genius and by nature a very through, rational, well educated and experienced in a wide range of industries and intelligent person as well as very helpful to others.  Far as I'm concerned, if he can't make these things work then they are garbage and unfit for purpose.  There is no way that he did anything but nurse the things with kid gloves and I know he was very disappointed  with them.  He is going to LA fork batteries and I doubt unless given to him he'd every consider  Lithium anything again.

Did he maybe just have bad luck? Maybe but aside from all the other failures people have had, he's had a failed system and been left very out of pocket through no fault of his own. Why would a sensible person do the same thing again and expect a different outcome?
Too big a risk for me because I know I'm never lucky.


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already some folks are very pleased with the reliability and lifespan of the very, very expensive BattleBorn 12V LFP batteries in marine applications (where size is a concern and cost is not so important.) 

I have also read glowing reports of the battlebornes and some not so good ones.  I think your statement of Cost not so Important is key here. The things are worth their weight in gold, or at least silver.  As you say, in marine applications, justifiable perhaps but for stationary storage, I do not see the point.  The cost of even 10 KWh of these things would probably by 30 or 50Kwh of LA.

I'm not even sure of the Benefits of Lipo in boats? Weight and size generally isn't an issue  In larger craft over 30 Ft and smaller don't carry many batteries anyway. Generally LA batteries are changed out annually because of the vibration boats experience. I really can't see the Lipos being more reliable and generally larger craft  have House and starting batteries that can be all paralleled for starting and  have reserve on the start batteries anyway.

Even if they took the replacement out to 2 or 3 years, I can't see the Lithiums being cheaper nor work out what the advantage is.
When these vessels carry couple of ton of Fuel, another ton or more of water and weigh 16T plus all up, can't even see what saving 2-300Kg of batteries is going to achieve. If they only have 1-2 Batteries, again, the weight saving would be lucky to be a 1% weight saving over all.

I know Lithiums are all the rage in the Caravanning/ RV game but weight savings there make sense.

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Lastly, I'll add that 3 or 5 W, 3.2V zeners do not provide a useful non-manual  balancing system- for many reasons, such as connecting and disconnecting them manually  is a farce,

Sounded like it to me as well simply because of the ability to forget the things while doing the balance and cook them this way. The rest sounded Hokum as well but I'm no electronics expert although it sounded suspect to me so I avoided going down that rabbit hole given the rest of the claims made I knew were complete and utter rubbish.


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  Likewise the absurd notion that only US made submarine lead acid batteries are good when I'm surrounded by off grid homes all reliably and affordably run on a variety of LA batteries.

I have no idea what a submarine battery is? I suspect it's nothing but a traction battery of a certain specification/ capacity.  I would bet they are used in other applications like telecoms backup etc rather than being made exclusively for subs. In any case, no matter how good they are, where do I and Joe public get them? Not a lot of Submarine  Supply stores round me as I think My Country only has half a dozen anyway so not going to be able to Nip down to  " Sub supplies are Us"  to grab a few.

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That is a well acknowledged fact, and it's why cell voltage monitoring is built into LFP packs; typically charging is disconnected when any cell goes to max voltage, and discharging is disconnected when any cell goes low.  This to required save the cell(s) from destruction. 

No smart or Conscientious DIY pack builder I have read of does without a BMS. Pretty much like running an alternator in your car without a voltage regulator somewhere in the system.
Contrary to the claims made, lithiums are a LOT more sensitive to voltage and charging than LA and to run a Lipo pack without a BMS is merely a ticking time Bomb.

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The LFP prismatic cells were then destroyed by excessive voltage.  The cell balancing hardware was also destroyed by too high voltage.  So a complete and total loss of well over $10K worth of new LFP batteries, all a cascade of destruction from a MPPT failure.

I have read of similar occurrences. poor quality BMS that crap out in short order and take everything else with it. Even the preferred brands are not fool proof.  Another common one is not having the setting incorrect for the particular Chemistry.  Some DO LA, lipo, Lif4 etc and all have different parameters. Incorrect setting May not kill them straight away but 6 Months can be enough to render valuable packs useless.


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I'm hoping that the quality demands of automotive manufacturers will force rapid improvement in LFP quality and reliability, and the price of bargain B grade cells today will purchase reliable cells in the future.

This will happen eventually but I can't see it for a long time. The relevant thing for me is your next comment.....

 
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I accept that I may still live out my life on lead acid batteries, and at what is now $17/month battery bank replacement cost, I won't lose sleep over that.  I won't switch until it becomes clear that it's cheaper for me to do so.

I -MIGHT- have 20 years left in me.  I'd like to think so but I also think I'm kidding myself a bit.  That means that an LA pack is well within capability of seeing me out.... if they don't come round trying to drag me out my house against my will to administer " Medications" to save my life before hand.  I don't see my electrical needs being much different in time to come and with days of reserve capacity anyhow and a well oversized solar system as well as WVO fuelled generators, what works for me now is still going to be workable in 10 to 20 (Ha!) years.

The only real requirement to me for longevity is  Return on investment.  As long as I get a decen't run out of something so it's amortised cost is reasonable, then what is the problem?  You mentioned $17 month for your batteries.   50 Cents a day is cheap power in anyone's language.  I have friends in the country that pay $1.56  SUPPLY charge then they pay for the power they use on top of that.

I don't need something to last 20 years or even 10. As long as the cost per day/ month works out as being reasonable, I'm not concerned if I have to spend a day every 3 years replacing something and getting new.
If one looks at something like those Tesla power walls, I have never seen a scenario in any country where the cost price can be recoupled in 10 years.  See a lot of convoluted slight of hand accounting to say they can which is largely BS. The maths is real Simple.

They hold 13 KWH of energy useable.  Multiply 13 by the cost of power per KWH in your area. Work out the value of that power over 10 years. This will assume you use that full 13 Kwh every day which will never happen but for arguments sake... Does the value of the power saved outweigh the cost of the battery?  NO! Not even close.  Won't work out over 15 years and then you have lost about 20% I think it is in battery degradation according to official ( and VERY optimistic IMO) figures which blows the ROI out further.

Compare that with an LA pack one may well get their ROI in 4 years and the numbers are very different and even if the things lasted 5 Years you are still ahead over lipo. 
For me, the cost of the power I use from the grid would be almost $5K year.  2 years and I have my entire LA system paid off. 

To me, THAT is a return on investment. 
Anything that take 10+ years  is a Justification for a toy or a hobby, not a financially sound or worthwhile decision.

LA is a financially sound decision for storage. Lithium is merely grandstanding or trying to show off at this point in time.
Title: Re: Lithium cell balancing
Post by: Fred8 on November 03, 2021, 03:37:15 AM

"if" one were to rethink his energy needs, i think an argument can be made for the simplicity and low cost of a system based on the lowly golf cart battery.[/quote]

Where I am they are much more exy per KWH than fork packs.  I realise they are much cheaper elsewhere but one has to go with the best bang for the buck available to them.

If they were cheaper, it's only a matter of series/ paralleling them to get the required capacity.  as long as the DOD is not going to be too excessive, I see no problem with them.

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now if one wants all the modern creature comforts of modern living, then large traction batteries are likely something that is hard to beat, given a "complete" cost analysis (including risk factors).

This is what I have Found.  At my stage of life I want to enjoy the creature comforts. Not interested in living in a shoe box to save on bills, not interested in going round and unplugging wall packs to save 20W a day, I want to be comfortable and enjoy myself.  I have put up a very large for a domestic solar system and can generate more than I use so I use it within reason. Not stupidly, just so I don't have to concern myself with Running the AC or heating the whole house rather than walking from a warm room to a frigid one.

Fork pack allows these comfort with it's capacity and that of the solar I have and the backup gennys if I need them.

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"if" one gets really down in the weeds, and is willing to focus on an efficient system, with low cost per kw/hr, i can make a good argument for the automotive starting battery.

If the Number of batteries was sufficient so they operated within their design parameters of maybe an average discharge of only 10% DOD,  then again don't see why they wouldn't do.  Might only have a 3-4 yr life anyway but if the cost works out, nothing wrong with that.
A Large car battery is around 100 AH which you might have to rate as 10  useable so you would probably want a few but that's a storage not a technical issue.  Cost of leads and terminals between them all might be a significant cost though.

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we are probably still 10 years away from getting a quality lithium based battery, that is well protected and has a low risk of failure.

I believe quality Lipos are available now.  It's just the cost of them is excessive and people naturally gravitate to the cheapo 2nd grade cells  which are the good ones that failed in the manufacturing process to meet the required standard of the first quality cells.
If you want good lithiums, they are out there. If you want a good Car Rolls Royce is still available and similarly priced.
I'm happy with a Ford or Gm but some people now are buying those Chinese cars.  Good luck to them!

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in the end, it is hard to get a battery with the energy density of a gallon of fuel, as dependable, and at so low a price.

It is in fact IMPOSSIBLE by a very long measure to get a battery anywhere near the energy density of any liquid fuel.  I forget the number but 9x less energy on the best batteries to liquid fuel seems to stick in my mind.
Put it this way, a large car battery has roughly 1 Kwh of energy and that's Pulling it way down below where it's meant to go.  1 Litre of liquid fuel has 10 KWH of energy. Lithiums are better but still impractically short when compared to liquid fuels.

I saw a Doco on this a while back.  They compared some ultra High density battery to liquid fuels and got it to about a quarter I think it was of comparable density.  The battery had to be super cooled and was highly unstable.  They compared the energy density of other materials and said  a battery with the same energy density as liquid fuels is called a Bomb because of the energy that would have to be stored in it and the instability of such a chemical composition.

They also showed what it would take to make a long range airliner electric powered.  Not going to happen in my lifetime or anyone else's here I suspect. One thing they pointed out was the further a regular place goes the lighter it gets as fuel is burned off. With an electric, it's draging round the dead weight of the discharged battery cells the whole distance.  Makes a big difference to the energy required  for a long distance flight.

I have some battery chainsaws and they are great.  No lighter than a similar sized petrol  one but they have great torque and good endurance.  Matter of horses for courses.

Same with EV's. so much less range than an IC.  Say that and the tesla fans jump up saying the model whatever can go so far on a charge.
Not really.

I learned recently when talking to an owner the range is nothing like stated. Go over 80 KMH and the range plummets.  Highway speeds here is 100/110.  At that speed you loose 100km+ in range on these EV's,  Yes, if you want they can " Hyper Mile" along at 80 which is borderline if not flat out illegal on highways here causing an obstruction and adding hours to a journey one can do in an IC in one go, then yes it will go that far. Of course then a 4 hour trip turns into an over nighter by the time one allows for recharging.

I saw a new model release ( when it's available in 3 years or whatever)  where they said it would go this much further thanks to the battery break through. The only breakthrough was making the cell size larger and stuffing more of them in the vehicle. Wasn't a higher energy density, just different packaging.



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it appears to me that the lead acid battery still is a strong contender for stationary use.

It has few drawbacks in this application and a huge advantage in cost.

I spoke to someone about Buying some  UPS backup bank batteries that were being replaced earlier in the week.  A sizeable storage room full that are turned every 5 years.  They are being replaced with more LA because they are the most cost effective and reliable in the industry's view.

LA is a Long way from dead yet.
Not well suited to any portable use, the weight savings and power density of lipo  kill LA but for fixed uses, best bang for the buck by a long shot.

Title: Re: Lithium cell balancing
Post by: mobile_bob on November 03, 2021, 01:15:13 PM
my point with the automotive battery argument is as follows

prefaced by the tiny  home movement, wherein the owners are all about efficiency
and live in an area in northern climates where it is cold more months than not, poor wind resource, and less than optimum solar exposure.

lets add to that the owner being a 20-30 something that works away from home, leaves for work at around 7am and returns home at around 5pm,  about an hour to and from work, which is not too far fetched as tiny home folks generally like to be out of the city where they are less hampered by zoning and codes.

so he/she gets up at 6am to take a shower, make breakfast/coffee, and maybe start a load of clothes to be dried that evening.

the  house sits empty during the day,

basically with a little thought, one could get his heavy energy needs down to an hour in the morning and an hour in the evening.  during the rest of the day, the tstat is lowered and presumably heated with propane, the only power need would be the blower fan, and possibly the fridge topping off.

under such conditions, it would be a good use for a small cogen unit designed to fit the need.  provide the heavy load power in the morning, and evening (2hours per day) make the domestic hot water for washing, showering, cooking. and also used to top off a set of batteries that would be used to provide power during the day while the owner is gone and at night while he is asleep. all excess heat recovered could be used for domestic space heating, to lower the load on the furnace.

with such a system, a cogen might need no more than a 30 seconds to come on line and provide for those needs.  a bank of automotive batteries that are called upon to provide for that need twice a day should last at least 7years.   it would only need to cover the loads for the amount of time needed to get the engine driven cogen up and running, thereafter switchgear would switch the loads over to the cogen.

now 30 seconds is a long crank time for a car battery, however 2 such batteries would effectively be 15 seconds each, 4 such less than 8 seconds which is not a bad draw on a 4 battery bank that would presumably be in a more temperate environment, and with a much better controlled charging system than is typical of an automotive regulator.

the savings in avoided conversion steps, along with the batteries low cost due to economies of scale, all make for a relatively low cost of operation and certainly a lower first cost.

couple that with a small bank of golf cart batteries (again relatively cheap due to economies of scale), to provide power for the furnace blower, the fridge and maybe a few led lights used after the cogen shuts down in the evening to provide lighting and i think one could make a system that does about everything one would need to do given the constraints of location and size at a low cost and give a good life span.

mount a couple of those golf cart batteries in the commuter car, using a cord and anderson plug and you have a source of power that likely would reduce the fuel economy of the car below the margin of error.

add as much solar as one can afford, and the system gets much easier, even if the area is limited in that resource.

with a little more pencil work, i think the system could be scaled up so that a more comfortable space might work out just as well.

throw in a spouse and a pack of teenage kids, and all bets are off.  :)

bob g
Title: Re: Lithium cell balancing
Post by: mikenash on November 04, 2021, 05:27:33 AM
Following . . .  :)
Title: Re: Lithium cell balancing
Post by: Fred8 on November 06, 2021, 12:43:14 AM

couple that with a small bank of golf cart batteries (again relatively cheap due to economies of scale), to provide power for the furnace blower, the fridge and maybe a few led lights used after the cogen shuts down in the evening to provide lighting and i think one could make a system that does about everything one would need to do given the constraints of location and size at a low cost and give a good life span.

In that Atypical situation that would work.
How much and what size are the golf cart batteries where you are?  Definitely not cheap or all that readily available here. :0(

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add as much solar as one can afford, and the system gets much easier, even if the area is limited in that resource.

This is my philosophy.
I have all my inverters at least double overpaneled.  This has worked out VERY well.  At full output they would overload the HD wiring I put in but it's not about Max power, it's about getting decent power in bad conditions.  Winter fall off where I am is about 1/3rd the summer radiation so that is a big downrating for a start. Add in some Cloudy/ wet weather and I can be down to 10% of my generation I get on a clear summers day. THAT is what I am building for not the walk in 100Kwh a day I can get in summer.

The Kicker is being no natural or town gas, everything is electric so my demands can be huge compared to other people but not out of character for other homes in the area
By having plenty of solar you can run off what is being generated at the time ( on a decent day) without having to dip into your battery reserve.  If you can almost eliminate the day draw on the batteries by running " Direct" then the battery pack can be much smaller.
Thankfully I do not have to contend with Snow or daytime sub zero temps bugger that for a Joke!

Winter days can be mostly clear and beautiful and even the instant generation not too bad below what the summer is thanks to the over panelling  however, the real shortfall comes from having half the daytime hours.  It's the short days that hurt me the most not even the winter radiation fall off.  If I had the inverters running their rated capacity in panels, they would be useless pretty much.
IMHO, anything under 150% Panel to inverter ratio is a waste.  200% I consider to be the sweet spot.

For the most part you can get full rating out of the inverter which adds to more consistency of generation. If I had the inverters matching the panels I'd be getting stupid amperage on the good days and no more on the bad ones when I really need the power.

For batteries I have also found 3 and 4 aspect arrays to be best.  For me that's east, north, west and Flat.  For a battery you want a n even charging input not a peaked one. Getting the early charge after draining at night is also desirable.  Having  a flat panel(s) is beneficial for the overcast days although in that situation one is trying to gain fractions of a very diminished output to start with.

I usually set up a winter ground mount for a bit of extra boost which I tilt to the best winter angle. That was 3.5 Kw this year and a good help. Having perfect winter angle and alignment does give an edge on the roof mounted arrays which are simply NOT worth tilting not that I can do much about orientation. Then again, with one exception, they are all perfectly orientated at some part of the day. 

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throw in a spouse and a pack of teenage kids, and all bets are off.  :)

Again why I went Big.
Don't want to have to worry about the women's long showers, washing and drying one article of clothing in the early evening or late at night for the next day, leaving TV's on ( other than wearing out the TV for nothing) and all the other things that I got lectured about when I was a Kid for wasting power.   I have changed all the lights in the place to LED which use nothing but I still can't bear to see a light on in a room no one is in. Old habits die hard.

Title: Re: Lithium cell balancing
Post by: BruceM on November 06, 2021, 06:29:37 AM
"By having plenty of solar you can run off what is being generated at the time ( on a decent day) without having to dip into your battery reserve.  If you can almost eliminate the day draw on the batteries by running " Direct" then the battery pack can be much smaller."

I concur.  With present PV prices so good, while batteries still very expensive, the best economy is have lots of extra PV, modest battery bank and use a backup generator when necessary rather than oversize the batteries for more than a nights worth a power.  I"d like to add another 1500W array to face early morning sun.  I only use the inverter and it's big AC loads during sunny days; likewise cook electric on sunny days; only lights and electronics at night.  After destroying their first set of batteries in a year or two, most off grid newbies wise up and start doing simple power management.  Quite easy once you get into the swing of it.  Plenty of sun here in AZ, all year round.  Now that I have 2375 watts of PV, I haven't had to do any LIster/Generator battery charging even on cloudy days.



Title: Re: Lithium cell balancing
Post by: Fred8 on November 07, 2021, 12:24:26 PM

Now that I have 2375 watts of PV, I haven't had to do any LIster/Generator battery charging even on cloudy days.

A very modest amount of panels.  Beyond my imagination how you can manage that.  Then again, I spose your generation factor is a lot higher than mine but still....

Here you can buy good used 250W panels for  $50 very easily, often less if you are prepared to bargain. They come and go in supply but sometimes there are plenty around and sales are slow so if you haggle, You can get them cheaper.  I bought a batch of brand new panels earlier in the year for $16 ea for 290s.
They were leftovers a distributor had buried in the back of his warehouse and only was prepared to sell in one lot. I knew he'd have lots of enquiries for ones and 2 and other piddling amounts  so I made him an offer for the lot which he took.  Forked the set of 28 onto my truck still in the Boxes and he was happy to sell them.

 Took some of the 250's I had on my roof down and replaced them with these and sold the 250's at $40 ea.  ;D
The guy I was selling them to wanted to upgrade his 190W panels and go up to 6Kw.

Batteries here are never cheap. Most people selling them used want delusional money and they are usually pretty suspect as to condition anyway. There were loads of 190 Ah UPS backup batteries being offered here by some different sellers Recently.  All 10 Yo and they all wanted over $1.50 to $2 /Ah for them.  Too much of a risk for me.

I regard 5Kw as a basic solar array these days so your power management must be excellent if you can live Frugally enough to survive on half  of that.  5Kw sure would give you a nice buffer and enable you to do a lot more and concern yourself less. You could run your AC and electric stove much more often with less dependence on sunny days as well as not having to worry about using other appliances. 

I think a couple of days battery reserve is good. Would give me more peace of mind.  Having enough panels to  meet your needs even on bad days would be possible for people like yourself whom use little power but for me it would be impractical although quite the dream. I spose it would be a lot more practical if I had wood heating.
 That's by far my biggest power concern and of course comes when there is the least power to be had.  Summer of Course there is plenty of power so I can run the AC much as I like and don't have to worry.

I find if I run it hard and run it early in the day so the house never gets heat soaked I don't need it at night when the sun has gone.
Title: Re: Lithium cell balancing
Post by: BruceM on November 07, 2021, 04:42:19 PM
Yes, I can see how 5KW of PV would be a good figure for many with a home designed for grid power.  Cheap enough to do these days.

I have solar hot water for space and domestic heating, with an 800 gallon insulated storage tank, propane refrigerator and freezer and a superinsulated home.  My major power concern is the desire to do something useful with the excess power I have every day.  My batteries are full before noon every day, even in winter; on  dark days they're full by early afternoon (this is Arizona at 5600ft).  I just switch to propane cooking when it's dark.

People can and have been comfortable on WAY less PV than I have now;  I was quite happy with just 875W of PV that I had for 7 years, but back then I ran the Listeroid for all my AC needs and on dark winter mornings to bulk charge the batteries.

I haven't added wind power as I had originally intended, because PV has gotten so cheap.











Title: Re: Lithium cell balancing
Post by: Tanman on January 08, 2022, 10:43:20 PM
This guy is running a Nissan Leaf lithium pack and Chevy volt lithium packs in parallel with no BMS seemingly without issues:

https://youtu.be/VRI_BX1QtPs
Title: Re: Lithium cell balancing
Post by: BruceM on January 09, 2022, 08:33:18 AM
This video is unfortunately lacking in legitimate technical information, nothing about what he's doing for BMS/cell balancing, or how he divided up the high voltage packs.  Seems he's set up for a nominal 48V inverter/battery bank, but that's not clearly presented either.  He states he has only put this battery bank together a week ago; so has zero meaningful experience.

His diagram showing Volt and other battery packs in parallel is wildly misleading- the stock packs are high voltage and must therefor be reconfigured to a nominal 48V, if that is what his Magnum inverter is designed for.  I don't know the voltage of the stock battery sub-assemblies of cells are; he has left out all the useful information.






Title: Re: Lithium cell balancing
Post by: Tanman on January 09, 2022, 03:33:49 PM
If you want more technical information Im sure he would offer it. He has responded to some of my questions.

Looks like hes been running it that way (my first comment) for a while:

https://youtu.be/f36ElNs5WPA
Title: Re: Lithium cell balancing
Post by: BruceM on January 09, 2022, 06:14:08 PM
Thanks for that link, Tanman. 

It seems the Leaf modules are 2 series by 2 parallel cells , so he's reconfigured at the module level to a 48V nominal system, so roughly 7 modules in series.  Getting to use the intact modules is a big help.  Apparently the other batteries he's using have similar low voltage modules.  Leaf modules are designed to be connected to a BMS and I have found other efforts to replace that BMS.  The lack of cell level BMS and poor thermal management caused LOTS of Leaf battery failures, thus lots of used ones for sale.

It's very surprising to me that he's found the cells exceptionally well matched after 48 months with zero balancing other than the full voltage limiting by the PV charge regulator at the 7 series module level.  He is fuse limiting each 48V string to 30 amps or 1440 W; he mentions that for his system, 10 amp fuses would be sufficient, so he's only charge/discharging at below 10A or 480W per pack.

I agree with Will Proust on this.  He's a young enthusiast, not an engineer,  but his technical information is usually quite good.  His website is also a good resource for those interested in learning about and using Lithium batteries.
 
https://www.youtube.com/watch?v=rbkE4jxk3u8

I think most non-EE, non-electronics savy folks would be better served with the packaged 48 or 24V battery systems being sold for server racks.  Proust has some good evaluation videos on them.

For safety I'd sure want cell level high/low voltage monitoring and disconnect protection; and with that usually comes some sort of low current passive balancing.   If you don't have cell level voltage monitoring, when one of set of parallel cells dies as a short (which seems the most common reported failure mode), all the other cells in the 7 module (14 cell pairs) series string will be overcharged and this can lead to a thermal runaway and fire with lithium ion cells. 

It is encouraging that some of the automotive packs are designed with low voltage modules. Once LFP (greatly reduced fire hazard) automotive modules/blades are more available, at good prices,  it might be something I'd be willing to switch to. 

Best Wishes,
Bruce


 






 



Title: Re: Lithium cell balancing
Post by: photosolo on March 10, 2022, 07:38:57 AM
Im new here so apologies for being late to the discussion.
I'm living off grid in Mid-Wales (as of Sept 2022)
I built a 16s, 280AH LifeP04 battery with cells that I imported from China via Alibaba.
They were bought before Brexit & was in transit post brexit, so you can imagine the fun I had with that!

I gained most of my knowledge from Will Prowse and his Youtube & Forum.
The BMS I went with is called, 123BMS that was purchased from Holland
We are still in early days obviously but so far so good, touch wood !
With a decent charge on the battery our house can run for about 5/7 days depending. The system is without any Solar input at the moment as I still need to build the PV array. We have 4kw of solar to add when I get the time.
Title: Re: Lithium cell balancing
Post by: BruceM on March 10, 2022, 06:53:41 PM
Welcome to the forum and thanks for sharing your LFP battery experience, photosolo.  I assume you meant Sept 2021 as your start of off grid operation.

I checked out the  123BMS you selected and it is a very capable unit for those that want bluetooth, smart phone controlled BMS. It supports high voltage strings due to it's daisy chain serial communications and microcontroller per battery approach, and the 1 amp discharge current per cell should be good for larger capacity cells.  Getting the current per cell down to only 1.9 ma is very good for this type of design and is sign of a skilled designer.

I hope your PV installation will go smoothly!

Best Wishes,
Bruce



Title: Re: Lithium cell balancing
Post by: photosolo on March 13, 2022, 08:07:45 AM
Thanks Bruce, & yes well spotted September 2021 would be more accurate - Im still working on that time machine though!
The system is still in its teething stage, i'm just grateful nothing went bang!
It's a bit nerve racking setting up an off grid house, I'm just desperate now to get the Lister working properly again & of course building the PV array. Too many jobs & not enough time.... or money!